Rotor blades for a wind turbine must be finished according to certain criteria. For example, the outer surface of the rotor blade must be smooth, so that the aerodynamic properties of the rotor are not compromised. Furthermore, the surface of the rotor blade should be weather resistant. For these reasons, the surface of rotor blade must generally undergo one or more handling or processing steps such as sanding, painting, polishing, etc., before being transported to the site for mounting onto a wind turbine.
However, such a handling or processing steps can be problematic since rotor blades are becoming longer as advances in turbine design and blade manufacture allow for larger generators and larger rotor blade lengths. A rotor blade for a wind turbine can therefore exceed 70 m in length, measured from root to tip. Such a blade can easily weigh about 20,000 kg. A rotor blade is usually made of a composite material and is mostly hollow. The shape of the rotor blade alters along its length, for example from a cylindrical root section through a wider shoulder section to an airfoil portion, terminating in rather thin tip region. The differently shaped zones along the length of the blade, together with the weight of the blade and the care that must be taken to avoid any damage to the blade surface, result in expensive and time-consuming handling procedures.
In one known approach, the blade is held essentially horizontally by supporting the root end in some suitable manner, and using a holding apparatus to fix the blade at some point in the airfoil section. The known type of holding apparatus involves a stationary screw mechanism to apply a clamping force to the blade. The screw mechanism can be actuated electrically, pneumatically, or hydraulically. Since the blade is only held at two points, most of the blade surface is exposed. Access to the lower surface or the underside of the blade is relatively straightforward. However, the top side of the blade can only be accessed with difficulty. It may be necessary for workers to use cranes and/or moveable platforms in order to reach those surfaces. Alternatively, the screw mechanism can be opened to release the blade so that this can be rotated by one half turn, and then fastened again. Either way, the prior art techniques are time-consuming and therefore also expensive. Furthermore, the use of such a screw mechanism can result in damage to those regions of the blade about which it is clamped. Also, the securing of the screw mechanism relies exclusively on the manpower of the operator, so that a secure fastening cannot always be guaranteed.